Is JKR working on a Scottish crime novel?

Is JK Rowling writing a crime novel? According to crime novelist Ian Rankin (a neighbor of Jo's) she is. Rankin told a reporter at an Edinburgh literary festival that his wife had "spotted her writing in a cafe" and speculated whether she was "writing her Edinburgh detective novel."

UPDATE: Rankin has since said this was a joke perpetuated out of control by the press.